Photosynthesis uses carbon dioxide and respires in order to be carries out by autotrophs. In IBDP Biology, we are required to learn the different experiments that measures CO2, biomass, and oxygen.
The rate of photosynthesis can measured directly by the production of oxygen or the uptake of carbon dioxide or inderectly by an increase in biomass.
Rate of photosynthesis:
- Depletion of substrate which includes measuring how much carbon dioxide has been used or how much water is used
- Accumulation of a product - includes how much oxygen is produced or biomass is produced.
Carbon Dioxide:
- If you place a plant in an
enclosed space, then measure the available carbon dioxide before and after the experiment it will tell you how much CO2 has been used for photosynthesis.
- This means that CO2 will interact with water producing
bicarbonate and hydrogen ions. The acidity of the resulting solution will indicate the amount of CO2 present.
Oxygen:
- Photosynthesis produces oxygen and glucose. It is possible to measure how much oxygen a plant produces over time. It's easier with water plants.
- Place water plant in a jar with
water and shine a bright light on it. Collect the oxygen produced by placing a conical flask over the top and measure this. you can also count bubbles produced but this isn't super accurate.
- Independant variable:
light intensity
- Dependent variable:
oxygen volume against time
- Method
the collection of gas over water.
Biomass:
- Possible to measure how much heavier a plant is after photosynthesis.
- This means measuring the organic matter not the water.
- Therefore we need to determine the biomass by completely
dehydrating the plant before weighing it.
- The experiment would need to allow for the fact that no organism survives this treatment.
That's it!
Drafted by Venetia (Biology)